The present invention relates to a master cylinder device for use, for example, in a braking system or a clutching system for an automotive vehicle, and more particularly relates to a portless type such master cylinder device which is improved with regard to its operational and feeling characteristics.
The present invention has been described in Japanese Patent Application Ser. Nos. 60-232790 (1985) and 61-021733 (1986), filed by an applicant the same as the entity assigned or owed duty of assignment of the present patent application; and the present patent application hereby incorporates into itself by reference the text of said Japanese Patent Application and the claims and the drawings thereof; a copy is appended to the present application.
Further, the present inventors wish hereby to attract the attention of the examining authorities to copending patent application Ser. No. 918,974, which may be considered to be material to the examination of the present patent application.
In, for example, Japanese Patent Laying Open Publication Serial No. 57-41247 (1982) and Japanese Patent Laying Open Publication Serial No. 59-96045 (1984), neither of which is it intended hereby to admit as prior art to the present patent application except to the extent in any case required by applicable law, there is disclosed a portless type master cylinder device, for example for a braking or clutching system for a vehicle such as an automobile, which has a body within which is formed a cylinder bore, with a piston member being fitted in the cylinder bore so as to be slidably movable from an initial axial position therein which said piston member is at when not impelled by the brake or clutch pedal of the vehicle to which this master cylinder device is fitted, a pressure chamber being defined by said piston member in cooperation with the cylinder bore, and in which an intake valve communicates between the cylinder chamber and the fluid reservoir, this intake valve being opened when the piston member is in its initial axial position while said intake valve is closed when the piston member moves through more than a determinate relatively small axial distance from its said initial axial position. Thereby, when the brake or clutch pedal of the vehicle is not substantially depressed and accordingly the piston member is in its initial axial position, the intake valve allows brake or clutch fluid to be supplied freely from the fluid reservoir into the cylinder chamber, thus to replenish said cylinder chamber. However, when the brake or clutch pedal of the vehicle is progressively depressed, the piston member is progressively displaced from its said initial axial position so as to reduce the volume of said cylinder chamber, and initially said intake valve only slowly and progressively approaches the closed condition, to become completely closed only when said piston member has moved through said determinate relatively small but yet somewhat considerable axial distance from its said initial axial position. Thereafter, the brake or clutch fluid in said pressure chamber is squeezed, to be ejected therefrom towards the braking or clutching system of the vehicle in a per se conventional manner. Such a portless type master cylinder device dispenses with any port or ports in the side of the cylinder bore which are required to be traversed by the land or lands of the piston member during its stroke, substituting the action of the above described valve for the action of said port or ports, and accordingly the durability of the master cylinder device is enhanced.
However, this type of portless type master cylinder device is fraught with problems which will now be outlined. As outlined above, as the brake or clutch pedal of the vehicle is progressively depressed and the piston member is progressively displaced from its said initial axial position so as to reduce the volume of said cylinder chamber, since initially said intake valve only slowly and progressively approaches the closed condition until said piston member has moved through said determinate relatively small but yet somewhat considerable axial distance from its said initial axial position, thereby during this initial movement of the piston member no actuation of the braking or clutching system for the vehicle is performed, and instead brake or clutch fluid is expelled from the pressure chamber back towards the fluid reservoir, which is quite inappropriate at this time. This causes the phenomenon of so called empty or inactive piston stroke, and increase in the pressure in the pressure chamber is delayed to a unduly great extent from the position and the time that the brake or clutch pedal of the vehicle is initially depressed. Thus, the operational feeling for the brake or clutch pedal is worsened, and a good brake or clutch response cannot be obtained.